Composition and method for suppressing vapor loss of volatile hydrocarbons

ABSTRACT

A very effective composition for inhibiting vapor losses of stored hydrocarbons comprises a mixture of a surfactant, such as a foaming agent, and a polyglycol. Indeed a method for retarding evaporation of volatile hydrocarbons from a body of liquid hydrocarbon material is provided by forming a thin film of these compositions on the surface of the body of liquid hydrocarbons.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to techniques for minimizing the evaporativelosses of stored hydrocarbons. In particular, the present invention isconcerned with suppressing the volatilization of hydrocarbons containedin petroleum products such as crude oil.

2. Background of the Invention

In the past, petroleum products, particularly crude oil, have beenrelatively inexpensive commodities with the result that conservation ofthese commodities was never of great consequence. In very recent years,however, increased world demand for all natural resources hassubsignificantly altered the prior supply demand relationships so thatlosses of hydrocarbons from evaporation is deemed quite serious, notonly from an environmental point of view but also from a conservationpoint of view. Indeed, this concern for preserving our natural resourcesapplies not only to petroleum hydrocarbons but to all volatile liquids.

In the description to follow, reference will be made primarily tosuppressing the loss of hydrocarbons by vaporization from crude oils;however, it is to be understood that crude oil is merely one example ofa hydrocarbon which contains sufficient amounts of volatile componentswhich will undergo vaporization in substantial amounts during storage.

As will be appreciated, crude oil contains a very wide spectrum ofhydrocarbons ranging from those which have very high boiling points tothose which would exist in the vapor state if they were isolated.Indeed, it is the presence of these latter materials that contributes tothe significant vapor pressure of crude oil.

There have been a number of techniques suggested in the past forinhibiting the vaporization of hydrocarbons. For example, in U.S. Pat.No. 1,985,491, it is suggested that a fatty acid soap be mixed withwater and then beat into a froth with a vigorous air blast. The froth,thereafter, is spread on the surface of oil, so as to minimizeevaporation and oxidation of the oil.

In U.S. Pat. No. 2,822,238 evaporation of volatile nonaqueous liquidproducts is retarded by floating small hollow particles, wet by water,on the surface of the volatile liquid.

In U.S. Pat. No. 2,907,627, a technique is disclosed for inhibitingvapor loss by spreading a synthetic resin plastic such as a polyurethaneon the surface of the crude petroleum. In contrast, thereto, U.S. Pat.No. 3,421,838 discloses the use of rubber cement as a vapor barrier forvolatile petroleum products.

Other techniques suggested, inhibiting vaporization of hydrocarbonmaterials include the use of a gelling material to create an integralroof on an oil tank. In this regard see U.S. Pat. No. 3,639,258. Mentionshould be made also of the technique of preventing hydrocarbon lossesduring the loading of vessels by use of an aqueous foam which is stableduring the period corresponding to that required for loading. For thistechnique, see U.S. Pat. No. 3,850,206. These last two techniques forinhibiting vaporization of hydrocarbons have more limited applicabilitythan the above-mentioned techniques. Moreover, there still remains aneed for simple, inexpensive and widely applicable techniques forinhibiting the loss of vapor from petroleum hydrocarbons.

SUMMARY OF THE INVENTION

This invention contemplates vaporization retarding compositions whichwhen applied to the surface of a body of hydrocarbon liquid, forms aneffective film type barrier inhibiting evaporation. Thus, in one aspectof the present inventions, there is provided an evaporation retardingmixture capable of forming a continuous stable film over the surface ofa body of liquid hydrocarbon material comprising a surfactant and apolyglycol. The surfactant employed in the composition of the presentinvention is a surfactant which is substantially hydrocarbon insoluble.It must be a material which has the ability to pack tightly and toorient itself perpendicularly to the surface of the liquid hydrocarbonmaterial being treated. Finally, the surfactant is one having ahydrocarbon moiety containing about 16 carbon atoms in a linearaliphatic group. The polyglycol is selected from a wide range of liquidpolyhydroxy alkanes, including polyethylene glycols, polypropyleneglycols, and the like. The preferred polyglycol of the present inventionhas a molecular weight generally in the range of about 100 to about1200. Preferably, polyethylene glycol having a molecular weight of about400 is the preferred polyglycol. The evaporation retardant compositionsof the present invention will contain about 5 wt. % to about 50 wt. % ofpolyglycol based on the total weight of the mixture of polyglycol andsurfactant. Preferably, however, about 9 wt. % to about 11 wt. % of thepolyglycol will be employed.

In another embodiment of the present invention, there is provided amethod for retarding evaporation of volatile hydrocarbons from a body ofliquid hydrocarbon material by forming a thin film in the surface of thehydrocarbon of a vapor barrier material comprising a surfactant and apolyglycol.

These and other features in the present invention will be readilyappreciated upon a reading of the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a test tank used indemonstrating the effectiveness of the compositions of the presentinvention.

FIG. 2 is a graphic representation comparing the evaporation loss of asample of an untreated Southern Louisiana Crude oil with a sample of thesame crude treated in accordance with the present invention.

FIG. 3 is a graphic representation comparing the evaporation loss of asample of an untreated Arabian light crude oil with a sample of the samecrude treated in accordance with the present invention.

FIG. 4 is a graphic representation comparing the evaporation loss of asample of an untreated Nigerian Light Crude oil with a sample of thecrude treated in accordance with the present invention.

DETAILED DESCRIPTION OF INVENTION

As indicated hereinabove, the present invention is concerned generallywith suppressing hydrocarbon vapor loss from body of the hydrocarbonliquid by forming a continuous stable film of a barrier layer over tothe surface of the body of liquid hydrocarbon. In the detaileddescription which follows, however, specific reference will be made topreventing loss of volatile hydrocarbon compounds from crude oilalthough the present invention is applicable to a wide range of volatileorganic materials in addition to crude oils. Indeed, among the numeroushydrocarbon materials, the vaporization of which can be suppressed inaccordance with the present invention are liquid aliphatic hydrocarbons,liquid alicyclic hydrocarbons, liquid aromatic hydrocarbons and mixturesof these. Specific examples of volatile hydrocarbons, the vaporizationwhich can be substantially suppressed in accordance with the presentinvention include gasolines, heptanes, cyclohexanes, benzene, pyrideneand the like. The foregoing recitation of these hydrocarbon materialsthat can be effectively treated in accordance with the present inventionis not intended to be limiting, but merely exemplary of the wideapplicability of the present invention.

Generally speaking, hydrocarbon losses by vaporization are substantiallyreduced in accordance with the practice of the present invention byforming a continuous stable film over the surface of a body of liquidhydrocarbon which operates as a barrier to vapor loss. It has now beenfound that excellent evaporization retarding compositions for suchpurposes comprise a surfactant and a polyglycol.

The surfactant of the retarding mixtures according to the presentinvention are characterized by the following criteria. First, thesurfactant must be insoluble in the particular liquid hydrocarbon bodybeing treated. Second, the surfactant must have the ability to packtightly and to orient itself perpendicularly to the surface of theliquid hydrocarbon body. Third, the surfactant, to have sufficientresistance to hydrocarbon transfer from the surface of the liquidhydrocarbon body, must have hydrocarbon chain or moiety greater thanabout 8 carbon atoms, and more typically will have hydrocarbon moitiescontaining about 16 carbon atoms and greater.

It will be appreciated by those skilled in the art, the surfactants aregenerally classed as organic molecules containing both hydrophobic andhydrophilic groups in an organic molecule. Surfactants are furtherclassified as being strong wetting agents or as strong detergents. Inthe case of strong wetting agents the hydrophobic group tends to be inthe middle of the molecule. In contrast thereto, in strong detergents,the hydrophobic group is at the end of a hydrophilic group. Indeed, thehydrophilic group tends to be a linear hydrocarbon. In accordance withthe practice of the present invention, the surfactants that aresatisfactory are all strong detergents. More particularly, the mostpreferred surfactants are classified as foaming agents, i.e., they willform a foam if mixed with air or a suitable blowing agent.

Specific examples of eminently suitable strong detergents for thepractice of the present invention are: the sulfosuccinates such asdioctylsulfosuccinate, dihexylsulfosuccinate, ditridecylsulfosuccinate,diethylhexylsulfosuccinate; soaps such as sodium laurate, sodiummyristate, sodium palmitate, sodium stearate, and sodium oleate;non-ionic detergents such as the alkylaryl poly (oxyethylene) ethanols;cationic surfactants, such as amine salts such as cetyl trimethylammonium bromide, and quaternary ammonium compounds.

Many of the foregoing surfactants are available commercially as foamingagents. Consequently, it is one of the advantages of the presentinvention that commercially available foaming agents can be used as thesurfactant. Such foaming agents include Foaming Agent 8578, 8581, 8549and Foaming Agent ID20339 sold by Exxon Chemical Company U.S.A., NewYork City, N.Y.; Aer-O-Water sold by National Foam Systems, Inc. WestChester, Pa.; Light Water FC-200 Foam Concentrates sold by MinnesotaMining and Manufacturing Company, St. Paul, Minn.; and Igepal C0880 soldby Antara Chemicals, New York, N.Y.

The polyols suitable in the practice of the present invention includeliquid ethylene glycols such as triethylene glycol, polypropylene glycoland polyethylene glycol. Generally, the glycol is one which has amolecular weight in the range of about 100 to 1200 and preferably about400. The preferred polyglycol is polyethylene glycol.

In order to effectively inhibit the vaporization of hydrocarbons from abody of liquid hydrocarbon materials, it is necessary that theevaporation retarding mixture form a continuous stable film over thesurface of the body of liquid hydrocarbon material. While not wishing tobe bound by any theory, the polyethylene glycol components of theevaporative retarding mixtures of the present invention apparentlyassociate with the hydrophilic portion of the surfactant through weakvan der Waal forces thereby improving the impermeability of the film. Alimited lamella of the glycol is supported by surface forces. Byassociation with the hydrophilic moiety of the surfactant package, asandwich-like molecular configuration results. In any event, it has beendiscovered that the addition of polyethylene glycol to the foregoingabove-mentioned surfactant provides an effective evaporation retardingmixture which is capable of forming a continuous stable film over thesurface of a body of liquid hydrocarbon material.

In the practice of the present invention, generally from about 5 to 50wt. % of polyglycol based on the total weight of the evaporativeretarding mixture is employed. It is preferred, however, that from 9 to11 wt. % of polyethylene glycol as the glycol be used.

In applying the evaporation retarding mixture to the surface of a liquidhydrocarbon body, the mixture may be spread over the surface of theliquid hydrocarbon body by a convenient means. In the practice of thepresent invention, it is particularly preferred, however, that theevaporation retarding mixture be applied to the hydrocarbon body as afine aerosol spray. Application in the form of a fine aerosol spraytends to more effectively utilize the material in film forming andminimizes the amount which may sink through the liquid hydrocarbon.

The amount of evaporation retarding material applied to the surface ofthe liquid hydrocarbon bodies is not critical. It can be applied inalmost any amount sufficient to form a continuous thin film of theevaporation retarding mixture on the surface of the liquid hydrocarbonbody. For most effective retardation of evaporation, however, themixture will be applied in amounts sufficient to provide a filmthickness greater than 70 monolayers and preferably in an amount rangingfrom about 210 to 350 monolayers. Thus, it will be readily appreciatedby persons skilled in the art that the amount of material needed to forman effective barrier is relatively very small. Indeed, to form a filmthickness of approximately 350 monolayers on the cargo of a 90,000 tontanker, only about 31/2 gallons of the evaporative retarding mixturewould be required.

The unique features of certain aspects of the present invention arebrought out in the following examples which are strictly illustrativeand not to be construed as limiting in scope.

EXAMPLE 1

A series of tests were conducted using an open beaker that had adiameter of 2 inches. Some beakers were charged solely with ahydrocarbon liquid. Other beakers were charged solely with a hydrocarbonliquid and a commercially available foaming agent. In yet other beakers,liquid hydrocarbon was charged along with the evaporation retardantcompositions of the present invention. The amount of hydrocarbon loss,was determined over a period of time. Test data and the results from thetest are set forth in Table 1. It should be noted that in these tests,one drop (0.05 ml) of the evaporation retardant mixture was applied tothe surface of the hydrocarbon body. This 0.05 ml of retardant mixturerepresents a thickness of approximately 6000 monolayers of material.However, this does not represent the minimum effective thickness for themixture since a portion of the droplet in these tests did not remain onthe surface. In some instances, a portion of the droplet decended intothe liquid being tested.

                                      TABLE I                                     __________________________________________________________________________               Amount           Amount                                            Test       of Test          of Retard                                         No.                                                                              Hydrocarbon                                                                           Hydrocarbon                                                                          Retardant Mixture                                                                       Mixture                                                                            % Loss/Time elapsed, hrs.                    __________________________________________________________________________    1  Varsol.sup.1 #1                                                                        25 ml 0         0    50%/24 hrs.                                                                          100%/72 hrs.                          2  Varsol.sup.1 #1                                                                        25 ml Aer-O-Water/water                                                                       .05 ml                                                                             0%/24 hrs.                                                                           0%/36 hrs.                                              1:1                                                         3  Cyclohexane                                                                           120 ml 0         0    100%/6 hrs.                                  4  Cyclohexane                                                                           120 ml Aer-O-Water/Water                                                                       .05 ml                                                                             0%/24 hrs.                                                                           0%/48 hrs.                                              1:1                                                         5  n-hexane                                                                              100 ml 0         0    20%/2 hrs.                                                                           70%/7 hrs.                            6  n-hexane                                                                              100 ml Aer-O-Water.sup.2 &                                                                     .05 ml                                                                             12%/2 hrs.                                                                           40%/7 hrs.                                              Triethyleneglycol                                                             1:1                                                         7  n-hexane                                                                              100 ml Aer-O-Water.sup.2 &                                                                     .05 ml                                                                             20%/2 hrs.                                                                           70%/7 hrs.                                              water 1:1                                                   8  n-hexane                                                                              100 ml 0         0    30%/1 hr.                                                                            100%/5 hrs.                           9  n-hexane                                                                              100 ml Light Water.sup.3                                                                       .05 ml                                                                             17%/1 hr.                                                                            60%/5 hrs.                            10 n-hexane                                                                              100 ml Light Water.sup.3 /                                                                     .05 ml                                                                             8%/1 hr.                                                                             46%/5 hrs.                                              Triethylene                                                                   Glycol, 1:1                                                 11 Benzene 100 ml 0         0    90%/24 hrs.                                  12 Benzene 100 ml Aer-O-Water/                                                                            0    20%/24 hrs.                                                    Triethylene                                                                   Glycol 1:1                                                  13 Kuwait  100 g  0         0    6.8%/24 hrs.                                    Crude Oil                                                                  14 Kuwait  100 g  Aer-O-Water.sup.2 /                                                                     .05  0.6%/24 hrs.                                    Crude Oil      Triethylene                                                                   Glycol, 1:1                                                 15 So. La. Crude                                                                         100 g  0         0    2.8%/7 hrs.                                  16 So. La. Crude                                                                         100 g  Aer-O-Water.sup.2 /                                                                     .05  0.1%/7 hrs.                                                    Triethylene                                                                   Glycol, 1:1                                                 __________________________________________________________________________     .sup.1 Varsol is the trademark for a series of aliphatic solvents sold by     Exxon Chemical Company, U.S.A., N.Y., N.Y.                                    .sup.2 Aer-O-Water is the trademark for a foaming agent sold by National      Foam Systems Inc., West Chester, Pa.                                          .sup.3 Light Water is the trademark for a foaming agent sold by Minnesota     Mining & Manufacturing Company, St. Paul, Minnesota.                     

EXAMPLE 2

This test illustrates the unique effectiveness of the evaporationretardant mixture of the present invention. In this test, a number ofsamples of crude oil were placed in an open 120 ml beaker and allowed tostand for 24 hours at ambient conditions. In each of these tests, 0.05ml of various surface active agents were applied to the surface of thecrude oil. For comparative purposes, several samples were maintaineduntreated. For 24 hours, the loss of crude oil was measured. The resultsof these tests are given in Table II below. As can be seen from thedata, commercially available foaming agents which also are strongdetergent surfactants are not totally effective alone in suppressingvapor loss. Indeed, the commercially available foaming agent, LightWater, was approximately only 50% effective in suppressing vapor lossfrom both South Louisiana and Kuwait Crude oil. In contrast, thereto,the Aero-O-Water foam formulation was only slightly effective for theSouth Louisiana crude oil but was highly effective for the Kuwait Crudeoil. This latter result was possibly due to the indigenous surfactantssuch as porphyrins that are known to be present in Kuwait crude oil.These compounds theoretically can combine with the Aer-O-Watersurfactant and result at a more effective barrier film. Nonetheless, ascan be seen, the addition of polyethylene glycol is highly effective inenhancing the evaporative retardant capabilities of the surfactants.

                  TABLE II                                                        ______________________________________                                                                          Weight                                      Test No.                                                                              Crude Oil Film Forming Material                                                                         Loss, grams                                 ______________________________________                                        1       So. La.   Aer-O-Water.sup.1                                                                           10.4                                          2       So. La.   0             12.2                                          3       So. La.   Light Water.sup.2                                                                           5.8                                           4       So. La.   Aer-O-Water.sup.1 /Light                                                                    1.5                                                             Water.sup.2 /Polyethylene                                                     Glycol.sup.3, 1:1:1                                         5       Kuwait    0             10.1                                          6       Kuwait    Aer-O-Water.sup.1                                                                           .5                                            7       Kuwait    Light Water.sup.2                                                                           6.1                                           8       Kuwait    Aer-O-Water.sup.1 /Light                                                                    .4                                                              Water.sup.2 /Polyethylene                                                     Glycol.sup.3, 1:1:1                                         ______________________________________                                         .sup.1 Aer-O-Water is the trademark for a foaming agent sold by National      Foam Systems, Inc. West Chester, Pa.                                          .sup.2 Light Water is the trademark for a foaming agent sold by Minnesota     Mining & Manufacturing Company, St. Paul, Minn.                               .sup.3 The molecular weight of the polyethylene glycol used was 200.     

EXAMPLE 3

This example demonstrates the effective barrier film thickness onevaporation rate. In this particular test a 190 mm diameter evaporationdish was charged with 800 ml of commercially available unleadedgasoline. Varying thicknesses of the evaporation retardant mixture wasapplied to the surface of the gasoline and the amount of gasoline lostover a period of time was determined. For the purpose of this test, theevaporation retardant mixture consisted of Aer-O-Water, Light Water pluspolyethylene glycol in a weight ratio of 1:1:0.2. Further details of thetest and the results given in Table III below. As can be seen from TableIII, a film thickness of greater than 70 monolayers reduces evaporationloss; however, a film thickness of 210 monolayers and greater is mosteffective. Indeed, it is particularly preferred that the film thicknessbe at least 350 monolayers.

                  TABLE III                                                       ______________________________________                                        EFFECT OF BARRIER FILM THICKNESS                                              ON EVAPORATION RATE                                                           190 mm diameter evaporation                                                   dish                                                                          Exxon Unleaded Gasoline                                                       Elapsed Time, Hrs.                                                                              0     0.5    1   2   3   6   7                              Monolayer Film                                                                Applied,  Thickness In                                                        Microliters                                                                             Monolayers  Evaporation Loss, Percent                               ______________________________________                                        0         0           0     10   16  25  31  42  46                           5         35          0     7    12  22  35  40  41                           10        70          0     6    10  20  27  40  42                           30        210         0     0     1   4   8  18  21                           50        350         0     0     0   0   0   0   0                           ______________________________________                                    

EXAMPLE 4

In order to simulate field conditions to some degree, steel containersof approximately 5 gallon capacity were constructed as showndiagrammatically in FIG. 1. These steel containers had baffles extendingdownwardly from the top of the steel container to approximately midpoint. A vent, approximately 1/2 inch in diameter, was provided at oneend of the upper surface of the steel tank. Each tank was charged withequal amounts (approximately 4 gallons) of a crude oil and rockedrepetitively through an angle of ±10° over the period of the test. Ascan be seen in FIG. 1, the internal baffles extended sufficientlydownwardly into the test liquid so that as the containers were slowlyrolled, the baffles would penetrate the surface of the test liquid andpromote a pumping of the vapors through the vent as the vapor space wascompressed during the rolling action. The test tank was rocked 180 timesper hour. In this series of these tests, the oil was sprayed with 0.8 mlamount of an evaporative retardant mixture consisting of Aer-O-Water,Light Water and polyethylene glycol in the weight ratio of 1:1:0.2 in anamount sufficient to provide the oil with a film thickness of from about500 to 1000 monolayers on the surface of the oil. The results of thesetests are set forth graphically in FIGS. 2 through 4.

What is claimed is:
 1. An evaporation retarding mixture capable offorming a continuous stable film over the surface of a liquidhydrocarbon body consisting essentially of: a surfactant or mixture ofsurfactants and a polyglycol, said surfactant or mixture of surfactantsbeing selected from materials that are insoluble in the liquidhydrocarbon body, which have hydrophobic moieties at the end ofhydrophilic hydrocarbon groups having greater than 8 carbon atoms andwhich materials are capable of forming stable foams with air and waterand said polyglycol being selected from dihydroxy derivatives of linearaliphatic hydrocarbons having a molecular weight of from about 100 toabout 1200, the amount of polyglycol in said composition ranging fromabout 5 wt. % to about 50 wt. % based on the total weight of theevaporation retarding mixture.
 2. The composition of claim 1 wherein 50wt. % of polyglycol is present in said mixture.
 3. The mixture of claim1 wherein the polyglycol is selected from triethylene glycol,polyethylene glycol and polypropylene glycol.
 4. The mixture of claim 2wherein the polyglycol is triethylene glycol.
 5. The mixture of claim 1wherein the polyglycol is polyethylene glycol having a molecular weightof about
 400. 6. The mixture of claim 1 wherein the surfactant has 16carbon atoms with hydrophilic portion of the molecule.
 7. Thecomposition of claim 1 wherein the surfactant is a sulfosuccinate.
 8. Acomposition for use in forming a continuous film on the surface of crudeoil to suppress evaporation thereof consisting essentially of:surfactant or mixture of surfactants in combination with a polyglycol,said surfactant or mixture of surfactants being selected from materialsthat are insoluble in the crude oil, which have hydrophobic moieties atthe end of hydrophilic portions of the molecules, which hydrophilicportion has between 8 and 16 carbon atoms, and which surfactant ormixture of surfactants is capable of forming stable foams with air andwater, said polyglycol being selected from dihydroxy derivatives oflinear aliphatic alkanes having molecular weights of from about 100 toabout 1200, the amount of polyglycol being in the range of from 5 wt. %to about 50 wt. % based on the total weight of the mixture.
 9. Thecomposition of claim 8 wherein the polyglycol is a polyethylene glycolhaving a molecular weight of about
 400. 10. The composition of claim 1wherein the amount of polyglycol ranges from about 9 wt. % to about 11wt. % based on the total weight of the mixture.
 11. A composition foruse in forming a continuous film on the surface of a liquid hydrocarbonbody to suppress evaporation thereof consisting essentially of: amixture of surfactants in combination with a polyglycol, said mixture ofsurfactants being selected from materials that are insoluble in theliquid hydrocarbon body, which have hydrophobic moieties at the end ofhydrophilic hydrocarbon groups and in which the number of carbon atomsin the hydrophilic portion of the molecule is between 8 and 16, andwherein the mixture of surfactants is capable of forming stable foamswith air and water, said polyglycol being selected from a hydroxyderivative of linear aliphatic alkanes having molecular weights of fromabout 100 to about 1200, the amount of polyglycol being in the range offrom about 9 wt. % to about 11 wt. % based on the total weight of themixture.